1. Field of the Invention
This invention relates generally to oilfield operations and more particularly to a subsea chemical injection and fluid processing systems and methods.
2. Background of the Art
Conventional offshore production facilities often have a floating or fixed platforms stationed at the water's surface and subsea equipment such as a well head positioned over the subsea wells at the mud line of a seabed. The production wells drilled in a subsea formation typically produce fluids (which can include one or more of oil, gas and water) to the subsea well head. This fluid (wellbore fluid) is carried to the platform via a riser or to a subsea fluid separation unit for processing. Often, a variety of chemicals (also referred to herein as “additives”) are introduced into these production wells and processing units to control, among other things, corrosion, scale, paraffin, emulsion, hydrates, hydrogen sulfide, asphaltenes, inorganics and formation of other harmful chemicals. In offshore oilfields, a single offshore platform (e.g., vessel, semi-submersible or fixed system) can be used to supply these additives to several producing wells.
The equipment used to inject additives includes at the surface a chemical supply unit, a chemical injection unit, and a capillary or tubing (also referred to herein as “conductor line”) that runs from the offshore platform through or along the riser and into the subsea wellbore. Preferably, the additive injection systems supply precise amounts of additives. It is also desirable for these systems to periodically or continuously monitor the actual amount of the additives being dispensed, determine the impact of the dispersed additives, and vary the amount of dispersed additives as needed to maintain certain desired parameters of interest within their respective desired ranges or at their desired values.
In conventional arrangements, however, the chemical injection unit is positioned at the water surface (e.g., on the offshore platform or a vessel), which can be several hundred to thousands of feet) from the subsea wellhead. Moreover, the tubing may direct the additives to produced fluids in the wellbores located hundreds or thousands of feet below the seabed floor. The distance separating the chemical injection unit and the locus of injection activity can reduce the effectiveness of the additive injection process. For example, it is known that the wellbore is a dynamic environment wherein pressure, temperature, and composition of formation fluids can continuously fluctuate or change. The distance between the surface-located chemical injection unit and the subsea environment introduces friction losses and a lag between the sensing of a given condition and the execution of measures for addressing that condition. Thus, for instance, a conventionally located chemical injection unit may inject chemicals to remedy a condition that has since changed.
The present invention addresses the above-noted problems and provides an enhanced additive injection system suitable for subsea applications.